Abstract: Global-scale deteriorations in coral reef health have caused major shifts in species composition and are likely to be exacerbated by climate change. It has been suggested that one effect of these observed and projected ecological changes will be lower carbonate production rates on coral reefs, which will impair reef growth potential, compromise their ecosystem functions, and ultimately lead to states of net reef erosion. However, quantitative data to support such assertions are limited, and linkages between the ecological state of reefs and their past and present geomorphic performance (in other words their growth potential) are unresolved. Using measures of gross and net carbonate production and erosion from 22 Caribbean coral reefs, we have recently shown that contemporary carbonate production rates are now substantially below those calculated for pre-disturbance and ‘healthy’ Caribbean reefs. On average, current production rates are less than 50% of pre-disturbance rates, and calculated accretion rates (mm yr-1) are also an order of magnitude lower within shallow water habitats compared to Holocene averages. A live coral cover threshold of around 10% is identified that is critical to maintaining positive production states. Below this ecological threshold many carbonate budgets become net negative and reef accretion stalls. Collectively, these data suggest that recent ecological declines are now propagating through the system to impact on the geomorphic performance of Caribbean reefs and will impair their future growth potential. However, an important constraint on more widespread reef structural decline can be identified in the form of significantly reduced abundances of reef eroding taxa and this, to some extent, is offsetting more dramatic impacts of coral cover loss. Overall, however, most Caribbean reefs appear to have vastly reduced capacity to keep up with rising sea levels, and thus those ecosystem functions most dependent on reef structures remain threatened.

Bio: Chris Perry is a Professor in Physical Geography and Director of Research for Geography at the University of Exeter, UK. He is a coral reef geoscientist whose research is focused on improving understanding of the response of coral reefs and reef islands to environmental and climatic change. Key areas of current research are aimed at improving understanding of rates and styles of coral reef growth, with a specific focus on terrestrial sediment-influenced nearshore environments;  on better understanding the timing of reef island development and on the sedimentary links between reefs and reef islands; and on quantifying rates of coral reef and marine carbonate production.